diff --git a/GirafAPI/Endpoints/ActivityEndpoints.cs b/GirafAPI/Endpoints/ActivityEndpoints.cs
index 0ef19b8..102ee18 100644
--- a/GirafAPI/Endpoints/ActivityEndpoints.cs
+++ b/GirafAPI/Endpoints/ActivityEndpoints.cs
@@ -26,7 +26,7 @@ public static RouteGroupBuilder MapActivityEndpoints(this WebApplication app)
 
                 return Results.Ok(activities);
             }
-            catch (Exception ex)
+            catch (Exception)
             {
                 return Results.Problem("An error occurred while retrieving activities.", statusCode: StatusCodes.Status500InternalServerError);
             }
diff --git a/GirafAPI/Endpoints/LoginEndpoints.cs b/GirafAPI/Endpoints/LoginEndpoints.cs
index 67db6b3..ef0952e 100644
--- a/GirafAPI/Endpoints/LoginEndpoints.cs
+++ b/GirafAPI/Endpoints/LoginEndpoints.cs
@@ -32,8 +32,8 @@ public static void MapLoginEndpoint(this WebApplication app)
 
                 var claims = new List<Claim>
                 {
-                    new Claim(ClaimTypes.NameIdentifier, user.Id),
-                    new Claim(ClaimTypes.Name, user.UserName)
+                    new Claim(ClaimTypes.NameIdentifier, user.Id ?? throw new ArgumentNullException(nameof(user.Id))),
+                    new Claim(ClaimTypes.Name, user.UserName ?? throw new ArgumentNullException(nameof(user.UserName)))
                 };
 
                 claims.AddRange(roles.Select(role => new Claim(ClaimTypes.Role, role)));
diff --git a/GirafAPI/Endpoints/OrganizationEndpoints.cs b/GirafAPI/Endpoints/OrganizationEndpoints.cs
index 92bf03a..7106494 100644
--- a/GirafAPI/Endpoints/OrganizationEndpoints.cs
+++ b/GirafAPI/Endpoints/OrganizationEndpoints.cs
@@ -25,14 +25,14 @@ public static RouteGroupBuilder MapOrganizationEndpoints(this WebApplication app
                         return Results.BadRequest("Invalid user id.");
                     }
 
-                    await dbContext.Entry(user)
-                        .Collection(u => u.Organizations).LoadAsync();
-
                     if (user.Organizations is null)
                     {
                         return Results.NotFound();
                     }
 
+                    await dbContext.Entry(user)
+                        .Collection(u => u.Organizations!).LoadAsync();
+
                     var organizations = new List<OrganizationNameOnlyDTO>();
                     foreach (var organization in user.Organizations)
                     {
diff --git a/GirafAPI/Endpoints/UserEndpoints.cs b/GirafAPI/Endpoints/UserEndpoints.cs
index 1289cb2..7d20e76 100644
--- a/GirafAPI/Endpoints/UserEndpoints.cs
+++ b/GirafAPI/Endpoints/UserEndpoints.cs
@@ -95,7 +95,10 @@ public static RouteGroupBuilder MapUsersEndpoints(this WebApplication app)
         group.MapPut("/{id}/change-password", async (string id, UpdateUserPasswordDTO updatePasswordDTO, UserManager<GirafUser> userManager) =>
         {
             var user = await userManager.FindByIdAsync(id);
-            var result = await userManager.ChangePasswordAsync(user, updatePasswordDTO.oldPassword, updatePasswordDTO.newPassword);
+            var result = await userManager.ChangePasswordAsync(
+                user ?? throw new ArgumentNullException(nameof(user)), 
+                updatePasswordDTO.oldPassword, 
+                updatePasswordDTO.newPassword);
             return result.Succeeded ? Results.Ok() : Results.BadRequest(result.Errors);
         })
         .WithName("ChangeUserPassword")
@@ -109,7 +112,9 @@ public static RouteGroupBuilder MapUsersEndpoints(this WebApplication app)
         group.MapPut("/{id}/change-username", async (string id, UpdateUsernameDTO updateUsernameDTO, UserManager<GirafUser> userManager) =>
         {
             var user = await userManager.FindByIdAsync(id);
-            var result = await userManager.SetUserNameAsync(user, updateUsernameDTO.Username);
+            var result = await userManager.SetUserNameAsync(
+                user ?? throw new ArgumentNullException(nameof(user)), 
+                updateUsernameDTO.Username);
             return result.Succeeded ? Results.Ok() : Results.BadRequest(result.Errors);
         })
         .WithName("ChangeUsername")
@@ -122,7 +127,7 @@ public static RouteGroupBuilder MapUsersEndpoints(this WebApplication app)
         group.MapDelete("/{id}", async (string id, UserManager<GirafUser> userManager) =>
         {
             var user = await userManager.FindByIdAsync(id);
-            var result = await userManager.DeleteAsync(user);
+            var result = await userManager.DeleteAsync(user ?? throw new ArgumentNullException(nameof(user)));
             return result.Succeeded ? Results.NoContent() : Results.BadRequest(result.Errors);
         })
         .WithName("DeleteUser")
diff --git a/GirafAPI/Entities/Users/GirafUser.cs b/GirafAPI/Entities/Users/GirafUser.cs
index 987f1a0..40ca1d8 100644
--- a/GirafAPI/Entities/Users/GirafUser.cs
+++ b/GirafAPI/Entities/Users/GirafUser.cs
@@ -7,9 +7,9 @@ namespace GirafAPI.Entities.Users;
 // Base class for users that stores data common between user types.
 public class GirafUser : IdentityUser
 {
-    [StringLength(20)] public required string FirstName { get; set; }
+    [StringLength(20)] [Required] public required string FirstName { get; set; }
     
-    [StringLength(50)] public required string LastName { get; set; }
+    [StringLength(50)] [Required] public required string LastName { get; set; }
     
     public ICollection<Organization>? Organizations { get; set; }
 }
\ No newline at end of file
diff --git a/GirafAPI/Extensions/ServiceExtensions.cs b/GirafAPI/Extensions/ServiceExtensions.cs
index 93d4c55..7ae5d3f 100644
--- a/GirafAPI/Extensions/ServiceExtensions.cs
+++ b/GirafAPI/Extensions/ServiceExtensions.cs
@@ -50,7 +50,7 @@ public static IServiceCollection ConfigureJwt(this IServiceCollection services,
             var jwtSettingsSection = configuration.GetSection("JwtSettings");
             services.Configure<JwtSettings>(jwtSettingsSection);
 
-            var jwtSettings = jwtSettingsSection.Get<JwtSettings>();
+            var jwtSettings = jwtSettingsSection.Get<JwtSettings>() ?? throw new ArgumentNullException(nameof(JwtSettings));
             var key = Encoding.UTF8.GetBytes(jwtSettings.SecretKey);
 
             services.AddAuthentication(options =>
diff --git a/GirafAPI/Mapping/UserMapping.cs b/GirafAPI/Mapping/UserMapping.cs
index c60d0d2..447d2fd 100644
--- a/GirafAPI/Mapping/UserMapping.cs
+++ b/GirafAPI/Mapping/UserMapping.cs
@@ -34,10 +34,10 @@ public static GirafUser ToEntity(this UpdateUserDTO user)
     public static UserDTO ToDTO(this GirafUser user)
     {
         return new UserDTO(
-            user.Id,
-            user.Email,
-            user.FirstName,
-            user.LastName
+            user.Id ?? throw new ArgumentNullException(nameof(user.Id)),
+            user.Email ?? throw new ArgumentNullException(nameof(user.Email)),
+            user.FirstName ?? throw new ArgumentNullException(nameof(user.FirstName)),
+            user.LastName ?? throw new ArgumentNullException(nameof(user.LastName))
         );
     }
 }